1. Field of the Invention
The present invention relates to an umbilical comprising a number of fluid pipes, electric wires and/or optical conductors, and filler material located at least partially around and between the fluid pipes and the wires/conductors. They are collectively gathered in a twisted bundle by means of a laying operation. A protective jacket encompasses the fluid pipes, the wires/conductors and the filler material. At least one load carrying element is located at a predetermined location in the cross section of the umbilical. Optionally, one or more fluid pipes constitute the load carrying elements.
The invention also relates to a method of manufacturing the umbilical.
2. Description of Background Art
It is to be noted that the invention finds use in both the more traditional umbilical and the relatively newly suggested power umbilical, i.e. an umbilical that is able to transfer large amounts of electric power between the sea surface and equipment located at the sea bed. This application relates to the more traditional umbilical, while the power umbilical is subject to a separate patent application filed on the same day as the present application. It is further to be noted that the present umbilical primarily is intended to be used for static purposes and its tensional capacity is first of all required during the deployment thereof, subsequently to be resting more or less stationary on the sea bed.
The traditional way to perform the laying operation of several elongate elements is for example shown in NO 174940 (WO 93/17176) and NO 971984. When looking into the figures in the first document, in particular FIG. 1, the machinery normally required to manufacture such umbilical is shown. As shown, the machinery is complicated, space demanding, voluminous, and accordingly very cost intensive. In addition, due to the size, the machinery necessarily needs to be stationary, i.e. be located in a large facility, preferably close to a harbor.
The machinery necessarily needs to have these dimensions in order to fulfil its functions, namely to be able to wind the elongate elements together into a bundle that extends helically in the longitudinal direction thereof having a predetermined laying length, typically 1.5 to 15 meters per revolution, depending on the intended application.
It has been a distinct desire from the industries to be able to manufacture an umbilical by use of considerably simpler machinery. In addition, there is a desire to have a mobile facility that can produce the umbilical at the site, or close to the site where the umbilical is to be installed. How to enable this, in consideration of the premises above? Some regards have been necessary to take, and in particular the ability of the umbilical to take up and withstand tensional loads. This is discussed below.
When such a bundle of elongate elements are subjected to tensional loads, for example during deployment on deeper waters, the twisted, or wound, elements will tend to “straighten out” or “twist open.” It is the load carrying elements in the cross section that are dedicated to take up the tensional loads. The load carrying elements can be pipes, steel wires or elements made of composite material, either in the form of individual composite rods distributed on the cross section or rods gathered in bundles. An example of composite material is carbon fiber.
With the now proposed solution for the laying operation of the umbilical, which simplifies the manufacturing process substantially, the load carrying elements will not necessarily be able to fulfil their function, namely be able to transfer substantial loads, or tensional loadings. They will, as indicated above, only tend to straighten out. However, such a new solution will require only a very simple machinery of manufacture compared with the traditional ones. So all the desires set forth above will be fulfilled. But as one will understand, a new problem is created—how to enable the load carrying function?
This is an acknowledged problem and in this respect we refer to U.S. Pat. No. 6,472,614 in the name Coflexip. In column 1, from the middle of the page and down, it is indeed described that the elements of the umbilical normally (traditionally) are wound together in the well known S-Z configuration, which means that it is wound alternating with shifting direction. Further, it is described that since the S-Z configuration cannot withstand substantial tensile stress without unwinding (as described above), additional layers of armouring (steel or KEVLAR, aramid fibers, for example) must be wound counter helically around this bundle to take up the tensile stress. The armoring consists of a plurality of steel wires or rods placed side by side with small pitch relative to the longitudinal axis of the umbilical.
In order to teach how this umbilical typically looks, U.S. Pat. No. 6,472,614 discloses that this is disclosed in API (American Petroleum Institute) specification 17E, “Specification for Subsea Production Control Umbilicals,” in particular pages 42, 43 and 44. Abstracts from this are shown in FIGS. 7-8 and are marked with “prior art”. It is further stated in U.S. Pat. No. 6,472,614, at the bottom of column 2, that there is no standard for steel tube umbilicals at this moment, but that it will come. This we understand as a confirmation of that the pipes that are shown on page 43 of the specification 17E are thermoplastic pipes—and not steel pipes as the present invention relates to.
Such is also included to illustrate the traditional way of thinking when it comes to S-Z laying (winding) combined with load carrying. This requires armoring rods that are helically wound (not S-Z) in at least two layers and each layer is wound in opposite directions to each other in order that they shall be able to act as the load carrying elements in the cross section.
As far as we know, no one has until this date carried out S-Z laying (winding) of the steel pipes in an umbilical, just because they perform the load carrying function and will, by applying axial loads of some magnitude, tend to straighten out (unwind), just as described in said U.S. Pat. No. 6,472,614. In addition, the steel pipes naturally are inherently rigid by nature and consequently intractable to handle in such a laying operation.
Another problem with this type of subsea umbilicals has been that pipes and cables need to be spliced relatively frequently, perhaps every 500 meters. This results in a substantial number of joints, if lengths of several tenths of kilometers are to be supplied. Every single splicing operation is time consuming. In complicated cross sections of the umbilical, it may take a couple of days to perform such a splicing operation.
Thus a challenge has been prevailing in the task to be able to manufacture substantial lengths of umbilicals having complicated cross sections and with fewer splices than before; in brief to achieve a more continuous and effective production. Similarly, as before, it is a demand that the umbilical can be coiled up on carousels or reels for shipping and transportation purposes.